Reactivity of para-benzynes in solution and in the gas phase

Investigation of organic monoradicals reactivity using surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) and self-assembled monolayer (SAM) approaches were used to investigate the reactions of organic monoradicals with methanol. An attempt was made to generate monoradicals from thiophenols and phenylmethanethiols substituted with bromine, iodine, and nitro groups by irradiation with UV light. Monolayers of radical precursors were deposited on SERS substrates, which were then immersed in methanol and irradiated for 1 and/or 3, 6, 12 and 24 h in a UV photochemical reactor. Pre- and postreaction SERS spectra were obtained by using a confocal Raman microscope and compared with the spectra of expected products of the radical reaction with methanol. Our studies have shown that the efficiency of monoradical generation is highly dependent on the chemical structure of the precursor. In addition, it is shown that both the SERS substrate and experimental conditions used strongly influence the obtained results.

Recent Advances in Mass Spectrometry-Based Structural Elucidation Techniques

Mass spectrometry (MS) has become the central technique that is extensively used for the analysis of molecular structures of unknown compounds in the gas phase. It manipulates the molecules by converting them into ions using various ionization sources. With high-resolution MS, accurate molecular weights (MW) of the intact molecular ions can be measured so that they can be assigned a molecular formula with high confidence. Furthermore, the application of tandem MS has enabled detailed structural characterization by breaking the intact molecular ions and protonated or deprotonated molecules into key fragment ions. This approach is not only used for the structural elucidation of small molecules (MW < 2000 Da), but also crucial biopolymers such as proteins and polypeptides; therefore, MS has been extensively used in multiomics studies for revealing the structures and functions of important biomolecules and their interactions with each other. The high sensitivity of MS has enabled the analysis of low-level analytes in complex matrices. It is also a versatile technique that can be coupled with separation techniques, including chromatography and ion mobility, and many other analytical instruments such as NMR. In this review, we aim to focus on the technical advances of MS-based structural elucidation methods over the past five years, and provide an overview of their applications in complex mixture analysis. We hope this review can be of interest for a wide range of audiences who may not have extensive experience in MS-based techniques.

Gas-Phase Reactivity of Phenylcarbyne Anions

Gas-phase reactivities of the phenylcarbyne anion and its four derivatives were studied using a linear quadrupole ion trap mass spectrometer. The phenylcarbyne anions were calculated to have a triplet ground state (singlet-triplet splittings of 4-9 kcal mol^-1), with the exception of the 4-cyanophenylcarbyne anion that has a singlet ground state (singlet-triplet splitting of -1.9 kcal mol^-1). Only the phenylcarbyne anions with a triplet ground state react with acetone and dimethyl disulfide via radical mechanisms. On the other hand, only the phenylcarbyne anion with a singlet ground state abstracts H₂O and H₂C═C═O from acetic acid via electrophilic addition of the reagents to the anion. Finally, two hydroxy-substituted phenylcarbyne anions (with triplet ground states) partially tautomerize with the assistance of reagent molecules to the more stable distonic phenylcarbene anions. This occurs via abstraction of a proton from the reagent by the phenylcarbyne anion to generate a neutral (triplet) phenylcarbene and a reagent anion, which is followed by proton abstraction from the hydroxyl group of the neutral phenylcarbene by the reagent anion to generate the distonic phenylcarbene anion in an excited triplet state. Experiments performed on deuterated hydroxy-substituted phenylcarbyne anions verified the mechanism. The reactivities of the distonic phenylcarbene anions were found to be quite different from those of the phenylcarbyne anions. For example, they were found to abstract CH₂ from acetonitrile, which is initiated by C-H insertion─typical singlet carbene reactivity.